1. Field of the Invention
The present invention relates to a puncher for punching holes through work pieces such as sheet and plate placed between a stationary member and a movable member and a puncher head to be used in the puncher.
2. Description of the Related Art
When an instrument board such as a switchboard, a distribution board or a control board is made to order, a ready-made box or case with no holes is worked to conform to individual needs. The ready-made case is not provided with holes for meters, breakers, switches etc. when it is delivered. The necessary holes have to be punched out for the instruments.
The usual process of making a hole on the face of a switchboard by a round puncher is this: The center of the hole is first marked by a center punch and then, with the tip of a drill placed at the mark, the drill is switched on to cut out a guide hole for the draw-back shaft of the puncher. The guide hole must be 2 to 3 mm larger than the draw-back shaft in diameter. If the guide hole is identical with the draw-back shaft in diameter, a doughnut-shaped cut-off scrap will adhere the draw-back shaft too hard to remove by hand after the punching work. For a draw-back shaft 10 mm in diameter, for example, a guide hole 13 mm in diameter is usually drilled.
But the problem is that it is difficult to punch an intended hole concentrically with the guide hole; the draw-back shaft tends to be eccentric with the guide hole, resulting in a deviation from the mark and a spoiled board. Even a 1 mm deviation would stand out especially on a board with a plurality of instruments mounted thereupon.